Vibrato is a slightly tremulous effect imparted to an instrumental tone for added warmth and expressiveness, consisting of slight and rapid variations in the pitch of the tone being produced. Stringed instruments, such as guitars, violins, violas, cellos, double basses, banjos, mandolins, etc., together with a few other instruments such as trombones, are unique in allowing the musician to produce any of a continuum of musical pitches by making slight variations in the position of fingers or in the configuration of the instrument. Among stringed instruments, this has led to the development and use of techniques to produce vibrato sounds by varying the position of the fingers along the strings.
Another way to produce vibrato sounds is by using a vibrato assembly that varies the tension of the strings while the fingers remain stationary. A conventional vibrato assembly (often called a tremolo tailpiece even though in stringed instruments tremolo usually refers to variations in the amplitude rather than in the pitch of the tone produced) has a bridge that rotates relative to the body of the stringed instrument about a knife-edge hinge or rolling ball bearings to produce variations in the tension of the strings and thereby variations in the pitch of the tone.
Previously known vibrato assemblies have several disadvantages. Knife-edge hinges and rolling ball bearings have friction that can produce wear on the pivoting surfaces and cause hysteresis (i.e., prevent the strings from returning precisely to their basic pitch). The pivoting of knife-edge hinges and rolling ball bearings produces undesirable noise and rumbling sounds that nearby electroacoustic pickups on electric stringed instruments detect and transmit to the amplifier. Knife-edge hinges and rolling ball bearings allow acoustic micro slip (i.e., sliding friction in the transmission of elastic strain waves) that prevents the efficient transfer of acoustic energy between the strings and the instrument body. This results in a loss of tonal quality (i.e., the number and relative intensity of the harmonics), frequency range, and sustain (i.e., an absence of energy loss that allows the string to vibrate freely). Also, because of the high line-contact or point-contact stresses present, even slight overloads can damage knife edges or ball-bearing races and thus cause increased friction, noise, and acoustic losses.
For the reasons previously discussed, it would be advantageous to have a vibrato assembly for stringed instruments that exhibits no wear or hysteresis, does not create extraneous noise, efficiently transfers acoustic energy from the strings to the instrument body, and withstands rugged use.
The present invention is a vibrato assembly in which all relative motion between its parts is achieved by means of elastic flexural members. It is applicable to instruments having one or more strings. It has a vibrato base attached to the instrument (e.g., the body or the neck of the instrument), a vibrato armature means for supporting a string, and an elastic flexure pivot for allowing relative movement between the vibrato base and vibrato armature that varies the tension of the string. (The present use of the term "armature" is consistent with its use as the name of the moving part in wire strain gages, electromechanical relays, etc.) An instrument can have a single vibrato that varies the tension of all the strings or the instrument may have multiple vibratos, as many as one per string, each varying the tension of a subset of the strings.
The present invention has numerous advantages. The absence of any sliding or rolling contact eliminates the problems of friction and wear. The lack of surface friction coupled with the inherent restoring moment of the flexure pivots results in very low hysteresis. If suitable materials are employed, the hysteresis will be essentially zero-the strings will return exactly to their basic pitch. The operational noise of high-quality flexure pivots is negligible in comparison with that of knife-edge hinges and rolling ball bearings and is undetectable by conventional electro-acoustic pickups. This vibrato assembly provides a robust path for transmission of acoustic waves from the vibrating strings to the instrument body with minimal attenuation (energy loss) and distortion, resulting in improved tonal quality, range, and sustain. Also, it can be made sufficiently rugged to withstand accidents and abuse without performance degradation. An additional advantage of the present invention is that tonal characteristics can be altered by employing different materials.